1. Field of the Invention
The present invention generally relates to the art of Multi-Chip-Module (MCM) circuit structures fabricated from Low-Temperature-Cofired-Ceramic (LTCC) tape, and more specifically to a monolithic microelectronic circuit package including an LTCC dielectric structure and an in-situ heat sink.
2. Description of the Related Art
An MCM package generally includes a monolithic dielectric structure consisting of a number of layers of insulating material which have conductor patterns, resistors and other electrical circuit elements formed on their surfaces. The layers are thermally fused together such that the circuit elements are buried in the structure. Vertical interconnects (vias) are formed through the insulating layers and provide interconnection of circuit elements on adjacent layers.
One or more microelectronic integrated circuit chips, dies, and/or discrete components are mounted on the surface of the dielectric structure, and are connected to the buried elements by wire bonds or other connection methods. In a flip-chip configuration, a surface of an integrated circuit chip or die on which bonding pads are formed faces the dielectric structure, and the bonding pads are connected to mating bonding pads on the dielectric structure by electrically conductive bumps.
LTCC tape is a desirable material for fabrication of MCM dielectric structures, having a material formulation including a mixture of glass and ceramic fillers or recrystallizable glass which sinters at about 850.degree. C., and exhibiting thermal expansion similar to alumina. The low-temperature processing permits the use of air fired resistors and precious metal thick film conductors such as gold, silver, or their alloys. It also allows processing of base metals such as copper in a nitrogen or reducing atmosphere.
A general treatise on LTCC technology is found in an article entitled "DEVELOPMENT OF A LOW TEMPERATURE COFIRED MULTILAYER CERAMIC TECHNOLOGY" by William Vitriol et al ISHM Proceedings 1983, pp. 593-598.
A drawback of conventional LTCC tape is its low thermal conductivity and corresponding inability to dissipate heat generated by high power electrical components. This has conventionally limited the application of LTCC dielectric structures to low power electronic devices which generate relatively small amounts of heat.
A method of providing heat sinking in an LTCC dielectric structure to enable the use of higher power electronic devices is disclosed in my prior U.S. Pat. No. 4,899,118, entitled "LOW TEMPERATURE COFIRED CERAMIC PACKAGES FOR MICROWAVE AND MILLIMETER WAVE GALLIUM ARSENIDE INTEGRATED CIRCUITS", issued Feb. 6, 1990 The heat sink arrangement includes a number of tightly packed, high thermal conductivity, vertically stacked or staggered vias which are formed through an LTCC dielectric structure for conducting heat away from a heat generating component. The heat sink has a thermal conductivity comparable to that of high purity alumina.
Although suitable for numerous applications, the process for fabricating the thermally conductive vias is complicated and expensive, and a large number of vias reduce the durability of the LTCC dielectric structure. The heat sink constituted by the vias is relatively inefficient, since the vias must be laterally separated from each other by portions of the dielectric structure.